Emulsions of Ionic Liquids

ABSTRACT

The present teachings provide emulsions using ionic liquids for separation of biomolecules and related methods, compositions, and devices.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/853,911 filed May 25, 2004.

FIELD

The present teachings relate to methods for creating an emulsion ofionic liquids and methods for separating mixtures of chemical and/orbiological components in the emulsions. The present teachings can alsorelate to methods for creating an emulsion in a capillary.

INTRODUCTION

Electrophoresis as known in the art of handling a biological sample caninclude a process of handling, such as concentrating and/or separatingcharged species in the biological sample. The term “biological sample”as used herein can refer to components in biological fluids (e.g. blood,lymph, urine, sweat, etc.), reactants, and/or reaction products, any ofwhich can include peptides, nucleotides, or other charged species. Oneexample of electrophoresis is capillary electrophoresis. Capillaryelectrophoresis devices can, for example, be used to separate variouscharged species present in a liquid sample, such as a biological sample.The charged species present in the biological sample migrate through thecapillary under an applied voltage created by a voltage source, such asan electrode wherein the ions are pulled through the capillary.

Emulsions can include at least one surfactant and at least two buffers,such as water and a non-aqueous solvent. One type of emulsion, commonlyknown as an oil-in-water (o/w) emulsion, has a continuous phase (water)and a disperse phase (droplets of non-aqueous solvent stabilized by asurfactant). Another type of emulsion, commonly known as a water-in-oil(w/o) emulsion, has a disperse aqueous phase and a continuousnon-aqueous phase.

Emulsions and solid phases, for example solid beads, are commonly usedin separation techniques from classical chromatography to micro-emulsionelectrokinetic capillary chromatography (MEEKC). The emulsions or beadsare created outside separation columns or capillaries and then insertedinto the columns or capillaries. However, the packaging of the emulsionor beads into small capillaries or, alternatively, in integratedmicrodevices can be very difficult. It can be desirable to form anemulsion inside a small capillary or integrated microdevice.

SUMMARY

In various embodiments, the present teachings can provide a method forproviding an emulsion in a capillary including introducing into thecapillary a composition including a buffer and an ionic liquid; andapplying a voltage across the composition to form an emulsion. Invarious embodiments, a method for creating an emulsion can includecontacting a sample including a solute with a composition including abuffer and an ionic liquid; and applying a voltage across thecomposition to form an emulsion.

In various embodiments, the present teachings can provide a method forcreating beads inside a capillary including inserting in the capillary acomposition including a buffer and an ionic liquid; applying a voltageacross the composition to form an emulsion; and solidifying the emulsiondroplets to form beads.

In various embodiments, a method for separating a solute from a samplecan include applying a voltage across a composition including thesample, an ionic liquid, and a buffer to form an emulsion; andseparating the solute from the sample. In various embodiments, a methodfor separating a solute from a sample can include applying a voltageacross a composition including the sample, a buffer, and an ionic liquidto form an emulsion; packing the emulsion droplets against a barrier;and stripping the solute from the emulsion.

It is to be understood that both the foregoing general description andthe following description of various embodiments are exemplary andexplanatory only and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate various embodiments.

FIG. 1 illustrates a cross-section of various embodiments of a capillarywith a buffer segment between two ionic liquid segments.

FIGS. 2A-B illustrate fluorescent images of an embodiment of the presentteachings showing formation of emulsion droplets in a buffer.

FIGS. 3A-B illustrate a fluorescent and actual image of an embodiment ofthe present teachings showing formation of emulsion droplets in abuffer.

FIG. 4 illustrates a fluorescent image of an embodiment of the presentteachings wherein the oligonucleotides are separated from the emulsiondroplets.

FIGS. 5A-B illustrate fluorescent images of an embodiment of the presentteachings showing the coalescing of emulsion droplets after a period oftime.

FIGS. 6A-B illustrate a fluorescent and an actual image of an embodimentof the present teachings wherein small and uniform emulsion droplets arepacked and seen under fluorescence light (FIG. 6A) and transmissionlight (FIG. 6B).

DESCRIPTION OF VARIOUS EMBODIMENTS

Reference will now be made to various exemplary embodiments, examples ofwhich are illustrated in the accompanying drawings. Wherever possible,the same reference numbers are used in the drawings and the descriptionto refer to the same or like parts. in various embodiments, asillustrated in FIGS. 1-5B, the present teachings can relate to methodsfor creating an emulsion in a capillary. In various embodiments, FIG. 1illustrates reservoirs 10 containing ionic liquid 12, electrode 14,capillary 16, and buffer 18. Capillary 16 can be shaped such that itsends are submerged below the surface of the ionic liquid 12 in thereservoir 10. Submerging the openings of capillary 16 provides acontinuous ionic liquid segment from the reservoir 10 and into thecapillary 16 on either end of a segment of buffer 18. The term “segment”refers to a section of liquid. Electrode 14 can be a platinum wire orany other appropriate material to apply a current across the ionicliquid segments and buffer segment. The material and dimensions of thecapillary device are illustrative and can be altered by one skilled inthe art of microfluidics to any material and dimensions. For example,the capillary can be used in an integrated microdevice, such as amicrofluidics device. FIG. 1 is illustrative and any configuration canbe used.

In various embodiments, channels, including microchannels can be usedinstead of capillaries. Microchannels can be desirable channels becausethey provide several advantages over capillaries. Microchannels canfacilitate manufacturing and manipulation of liquids by filling accessholes to prevent evaporation. The ionic liquid segment and buffersegment can be introduced by applying vacuum, centripetal forces, activeor passive capillary forces, and/or pressure.

A composition, for example, which can be used in the disclosedembodiments can include an ionic liquid and a buffer. The term “ionicliquid” refers to salts that are liquid over a wide temperature range,including room temperature. Ionic liquids have been described athttp://bama.ua.edu/˜rdrogers/webdocs/RTIL. Variations in cations andanions can produce millions of ionic liquids, including chiral,fluorinated, and antibacterial ionic liquids. The large number ofpossibilities can provide ionic liquid properties tailored to specificapplications. Ionic liquids can be desirable because they areenvironmentally-friendly alternatives to organic solvents forliquid/liquid extractions, catalysis, separations, and electrochemistry.Ionic liquids can reduce the cost, disposal requirements, and hazardsassociated with volatile organic compounds. Exemplary properties ofionic liquids include at least one of high ionic conductivity,non-volatility, non-flammability, high thermal stability, widetemperature for liquid phase, highly solvability, and non-coordinating.

The choice of cations and anions determine the physical properties (e.g.melting point, viscosity, density, water solubility, etc.) of the ionicliquid. For example, cations can be big, bulky, and asymmetric, possiblyresulting in an ionic liquid with a low melting point. As anotherexample, anions can contribute more to the overall characteristics ofthe ionic liquid, such as air and water stability. The melting point forionic liquids can be changed by structural variation of at least one ofthe ions or combining different ions.

Examples of ionic liquid cations can include N-butylpyridinium and1-alkyl-3-methylimidazolium (1,3-dialkylimidazolium; alkyl mim).Examples of anions can include PF₆ that is immiscible in water, and BF₄⁻ that is miscible in water depending on the ratio of ionic liquid towater, system temperature, and alkyl chain length of cation. Otheranions can include triflate (TfO; CF₃SO₂ ⁻), nonaflate (NfO;CF₃(CF₂)₃SO₂ ⁻), bis(triflyl)amide (Tf₂N; (CF₃SO₂)₂N⁻), trifluoroacetate(TA; CF₃CO₂ ⁻), and nonafluorobutanoate (HB; CF₃(CF₂)₃CO₂ ⁻). Otherexamples of ionic liquids can include haloaluminates such aschloroaluminate. Chloro- and bromo- ionic liquids can have largeelectrochemical windows because molten salts prevent salvation andsolvolysis of the metal ion species. Further examples of ionic liquidscan include 1-alkyl-3-methylimidazolium PF₆ such as1-decyl-3-methylimidazolium PF₆, 1-butyl-3-methylimidazolium PF₆, and1-ethyl-3-methylimidazolium with NO₃, NO₂, MeCO₂, SO₄, PF₆, TfO, NfO,BF₄, Tf₂N, and TA, N-alkylpyridinium chloride or N-alkylpyridium nickelchloride with C₁₂ to C₁₈ alkyl chains, and any variations of these asare known to one skilled in the art of ionic fluids. Other examplesinclude 1-ethyl-3-methylimidazolium bis(1,2-benzenediolato-O,O′)borate,1-ethyl-3-methylimidazolium bis(salicylato)borate,1-ethyl-3-methylimidazolium bis(oxalate)borate, and other compoundsdescribed in U.S. Pub. No. 2002/0015883 to Hilarius, et al., andN-alkyl-N′-alkoxyalkylimidazolium ionic liquids such as those describedin Japanese Publication 2002/003478.

Sources of ionic liquids include Aldrich (Milwaukee, Wis.), ElementisCorp. (Durham, UK), Sachem (Austin, Tex.), TCl (Tokyo, Kasei), and Quill(N. Ireland).

The term ‘buffer’ herein refers to liquids that do not mix with ionicliquids. The buffer facilitates movement of the charged species throughthe capillary by providing a transportation medium through which thecharged species travels. Buffers can be aqueous (containing water), orthey can be non-polar organic solvents such as DMF, DMSO, xylene,octane, perfluorodecalin, and other hydrocarbons that can be at leastpartially soluble with the biological material. Buffers can be aqueousor organic because ionic liquids can be hydrophilic or hydrophobic. Invarious embodiments, hydrophobic ionic liquid segments of1-butyl-3-methylimidazolium hexafluorophosphate (BMI PF₆) and1,2-dimethyl-3-butylimidazolium hexafluorophosphate (DMBI PF₆) fromSachem, Inc. (Austin, Tex.) can be used with aqueous buffer segments,and hydrophilic ionic liquid segments of 1-ethyl-3-methylimidazoliumtetrafluoroborate (EMI BF₄) and 1-ethyl-3-methylimidazoliumtrifluoromethanesulfonate (EMI TFMS) from TCl (Tokyo Kasei) can be usedwith non-polar organic solvent buffer segments.

The buffer segment can include a biological sample including a solute.The solute can be chosen from a particle, such as a silica particle oran inert particle, and a charged species, for example a positivelycharged species or a negatively charged species. For example, the solutecan be chosen from biomolecules and bioparticles. In variousembodiments, the term “biomolecules” refers to any molecule associatedwith a life function. Suitable non-limiting examples of biomoleculesinclude proteins, peptides, nucleotides, DNA, and RNA.

In various embodiments, the term “bioparticles” refers to particlesformed by, or useful in, any biological process. Suitable non-limitingexamples of bioparticles include cells, cell organelles, cellaggregates, tissue, bacteria, protozoans, viruses, and other smallorganisms.

In various embodiments, the solute can act as a “seed” or an initiatorof the formation of the emulsion. For example, the charged speciespresent in the solute can become associated with the emulsion droplets.The term “associated” and grammatical variations thereof as used hereinrefers to a situation wherein the charged species and the emulsiondroplets are joined or connected together in a spatial relationship. Forexample, the charged species can be bound to the emulsion dropletseither directly or indirectly. The association of the charged specieswith the emulsion droplet can transport charged species through theionic liquid by the emulsion droplet. For example, DNA can act as a seedto form emulsion droplets, which can associate with the DNA. Due to theapplied voltage, the associated emulsion droplets and DNA can then betransported to an electrode, such as a positive electrode of thecapillary, to form a compacted emulsion.

The biological sample can be adapted for at least one of PCR, ligasechain reaction, antibody binding reaction, oligonucleotide ligationsassay, and hybridization assay. The sample can then be detected by atleast one of absorbance, fluorescence spectroscopy, Raman spectroscopy,reflectance, and colorimetry.

In various embodiments, a composition including a buffer and an ionicliquid is introduced into a capillary. A voltage is then applied acrossthe composition to form an emulsion.

The voltage can be applied for a sufficient period of time for anemulsion to form. The voltage can be applied from 1 minute to 48 hours,for example from 1 minute to 24 hours, as a further example from 2minutes to 5 minutes.

The voltage applied across the composition can range from 100 v to 2000v, for example from 500 v to 1000 v. Depending upon the length of thecapillary, the electric field strength can vary. For example, theelectric field strength can range from 1 v/cm to 1000 v/cm. By varyingthe electric field, the solute can be transported through the ionicliquid. Moreover, once an emulsion is formed, the solute can becomedisassociated or separated from the emulsion droplets by increasingand/or reversing the voltage from the initial voltage used to create theemulsion.

In various embodiments, an emulsion can include emulsion droplets. Thesize, shape, electric charge, and polarizability of the emulsiondroplets can depend on several factors, including, for example, theproperties of the biomolecules or bioparticles present in the biologicalsample. For example, the size of the emulsion droplets can be controlledby at least one of the buffer composition, the current density, theionic liquid, and time. In various embodiments, the emulsion dropletscan range, for example, in size from 1 nm to 10 nm, such as in amicroemulsion. In various embodiments, emulsion droplets can range up tothe order of millimeters. For example, at an initial time T₀, theinitial emulsion droplets can be nanometer in size. However, at a secondtime, T₁, the size of the emulsion droplets can increase to millimetersin size. As the time progresses from an initial time T₀ to a time T₁,then it is believed that the emulsion droplets can solidify or coalesceto form larger emulsion droplets, as shown in FIGS. 5A-B. Moreover, theemulsion droplets cannot be the same size throughout the capillary, butcan vary in size.

In various embodiments, the charge of the emulsion droplets can becontrolled by the buffer composition, i.e., the emulsion droplets can bepositive, negative, or have no charge. The charge of the emulsiondroplets and the solute present in the buffer can be the same ordifferent.

The term “separation” and grammatical variations thereof as used hereinrefers to the process of separating charged species based on theircharge/size. Separation can result from differentiating the chargedspecies by charge/size ratio by using a separation polymer as known inthe art of electrophoresis. The term “polymer” as used herein refers tooligomers, homopolymers, and copolymers and mixtures thereof as known inthe art of polymer chemistry. For example, the polymer can be used to atleast one of stabilize the emulsion or help separate the charged speciesassociated with the emulsion droplets. In various embodiments, once theemulsion is formed, the emulsion droplets can be packed against abarrier. The solute, such as the charged species, can then bedisassociated or separated from the emulsion droplets by using standardtechniques. For example, the solute can be stripped from the emulsiondroplets by reversing the direction of the voltage applied across thecomposition, such as shown in FIG. 4.

The timing of emulsion droplet formation and charged species travel canbe correlated In the properties of the buffer as is known in the art ofelectrophoresis.

The emulsion droplets can be solidified to form solid phases, forexample beads. Once formed, the beads can be used in standardchromatography or as, for example, a filtration grid in microfluidicdevices. In various embodiments, the emulsion is formed at a firsttemperature, which is then decreased to a second temperature wherein theemulsion solidifies. For example, a composition including a biologicalsample, an ionic liquid, and a buffer can be at a first temperatureranging from 20° C. to 200° C. immediately prior to application of thevoltage. In various embodiments, the emulsion droplets can be solidifiedby providing an ionic liquid having a combination of ions resulting inthe solidification of the emulsion droplets.

In various embodiments, a reaction can be performed within the buffer.The term “reaction” refers to the process of reacting reactants to formreaction products within the buffer. A reaction can result fromproviding reaction conditions such as temperature changes to thereactants within the buffer. Several biological reactions are describedherein. In various embodiments, the charged species can be concentratedto provide better detection of the reaction products by absorbance,spectroscopy (fluorescence or Raman), reflectance, colorimetry and anyother detection known in the art of analysis of biological materials.

In various embodiments, the ionic liquid and buffer can be static orthey can be in a continuous segmented flow. In various embodiments,continuous flow can provide the ability to pass the segments flowingthrough a channel through different process conditions such as waterbaths or other heating/cooling devices to thermally cycle the segmentsas in polymerase chain reaction (PCR), for example.

In various embodiments, the present teachings can provide a device forsample preparation including a substrate with at least one capillarychannel. A capillary channel operates functionally like a capillary butis constructed by etching or cutting a volume into a portion of thesubstrate. The capillary channel can be difficult to fill with anemulsion. The present teachings permit introduction of the emulsion intothe capillary channel for samples preparation. A solution of ionicliquids and buffer can be introduced into the capillary channel suchthat an emulsion forms separating biomolecules and bioparticles. Atleast two electrodes can provide a voltage across the capillary channelto form the emulsion. In various embodiments, the device has a networkof capillary channels and a plurality of electrodes to provide multipleemulsions.

In various embodiments, the emulsion includes emulsion droplets withbiomolecules that can be separated from the bioparticles. In variousembodiments, the emulsion droplets are solid.

In various embodiments, the device includes other unit operations suchas PCR or ligase reaction for analysis, and detection of biomoleculeanalysis.

EXAMPLES

The following examples are illustrative and are non-limiting to thepresent teachings.

Example 1

FIGS. 2A-B are exemplary illustrations of various embodiments of theinvention. FIG. 2A illustrates an embodiment wherein a voltage wasapplied across a composition including a buffer, an ionic liquid, andoligonucleotides. In a period of minutes, the oligonucleotides appearedto associate with the small emulsion droplets. The oligonucleotides weredragged toward the positive electrode. As illustrated in FIG. 2B, nearthe ionic liquid/buffer interface, the emulsion droplets collided andfused, forming larger emulsion droplets. At higher voltages (e.g. 500 v)the oligonucleotides became disassociated with the emulsion droplets andcontinued to move toward the positive electrode whereas the emulsiondroplets moved toward the negative electrode.

FIGS. 3A-B are exemplary illustrations of various embodiments of theinvention. FIG. 3A illustrates the formation of emulsion droplets in abuffer wherein the emulsion was detected by fluorescence imaging. FIG.3B illustrates the formation of emulsion droplets in a buffer whereinthe emulsion was detected by transmitted light.

Example 2

A buffer, TRIS-EDTA with 0.5% of POP-6® (Applied Biosystems, FosterCity), containing a sample of oligonucleotides, a mixture of 30 and 90base oligonucleotides labeled with Lys, and an ionic liquid, a 50:50mixture of 1-butyl-3-methylimidazolium hexafluorophosphate (BMI PF₆) and1,2-dimethyl-3-butylimidazolium hexafluorophosphate (DMBI PF₆) fromSachem, Inc. (Austin, Tex.) were introduced into a capillary tube. Avoltage of 1000 v was applied for 20 minutes. The oligonucleotides actedas “seeds” for the formation of the emulsion droplets which thenassociated with the oligonucleotides. This is illustrated by FIG. 6Awherein the formation of small and uniformly packed emulsion droplets isseen under fluorescence light. FIG. 6B shows small and uniformly packedemulsion droplets seen under transmission light.

The oligonucleotides and associated emulsion droplets were packedagainst a barrier. The oligonucleotides disassociated from the emulsiondroplets when the voltage was changed from positive to negative asillustrated in FIG. 4.

Example 3

An emulsion was formed in a capillary as described in Examples 1 and 2.After an hour the small emulsion droplets began to coalesce as shown inFIG. 5A. After 24 hours, the emulsion droplets had coalesced into largerdroplets as shown in FIG. 5B.

For the purposes of this specification and appended claims, unlessotherwise indicated, all numbers expressing quantities, percentages orproportions, and other numerical values used in the specification andclaims, are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that can vary depending upon thedesired properties sought to be obtained by the present invention. Atthe very least, and not as an attempt to limit the application of thedoctrine of equivalents to the scope of the claims, each numericalparameter should at least be construed in light of the number ofreported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Moreover, all ranges disclosed hereinare to be understood to encompass any and all subranges subsumedtherein. For example, a range of “less than 10” includes any and allsubranges between (and including) the minimum value of zero and themaximum value of 10, that is, any and all subranges having a minimumvalue of equal to or greater than zero and a maximum value of equal toor less than 10, e.g., 1 to 5.

It is noted that, as used in this specification and the appended claims,the singular forms “a,” “an,” and “the,” include plural referents unlessexpressly and unequivocally limited to one referent. Thus, for example,reference to “a charged species” includes two or more different chargedspecies. As used herein, the term “include” and its grammatical variantsare intended to be non-limiting, such that recitation of items in a listis not to the exclusion of other like items that can be substituted oradded to the listed items.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to various embodimentsdescribed herein without departing from the spirit or scope of thepresent teachings. Thus, it is intended that the various embodimentsdescribed herein cover other modifications and variations within thescope of the appended claims and their equivalents.

1. A composition comprising: an emulsion, the emulsion comprising. asolute, wherein the solute comprises biomolecules; a buffer; and anionic liquid, wherein the emulsion is formed by applying a voltageacross the composition.
 2. The composition of claim 1, wherein theemulsion comprises droplets ranging in size from 1 nm to 10 mm.
 3. Thecomposition of claim 2, wherein the size of the emulsion droplets iscontrolled by at least one of the buffer composition, the currentdensity, and the ionic liquid.
 4. Solid beads formed by solidifying theemulsion of claim
 1. 5. The composition of claim 1, wherein the emulsionforms into droplets having an electric charge.
 6. The composition ofclaim 5, wherein the charge of the emulsion droplets is controlled bythe buffer composition.
 7. The composition of claim 1, wherein thesolute is a charged species.
 8. The composition of claim 7, wherein thecharged species is a positively charged species.
 9. The composition ofclaim 7, wherein the charge of the emulsion droplets and the solute isthe same.
 10. The method of claim 7, wherein the charge of the emulsiondroplets and the solute is different.